Wiehl/Szombathely, Germany — Unsprung agricultural and forestry vehicles are feared obstacles on the road, and not only at harvest time: their brakes can only be adjusted by hand – a rather fiddly, imprecise and risky guesswork. The EU has therefore tightened regulations. The answer from BPW is as simple as it is ingenious: with a patent-pending fully mechanical system, drivers now have the brakes quite literally in their hands.
Nowadays, agricultural and forestry machines and their drawbar trailers are anything but rustic: highly technically advanced and in many cases fully digitally integrated, they represent the cutting edge of the commercial vehicle industry.
Most drawbar trailers that usually operate between the field, forest and farm are fitted with suspensions that can measure the loading condition and automatically adjust the brake force accordingly. One risky exception however are unsprung drawbar trailers such as tilling or harvesting machines, fertilizer spreaders, seed drills – truly an “unstoppable” condition, as the axle load of a single-axle spreader can typically vary between 3,300 and 10,000 kilograms.
The EU has responded with the directive VO (EU) 2015/ 68. If these vehicles have varying loading conditions, they may only be towed at a maximum of 30 km/h. Approval for higher speeds is only granted when the brake force can be adjusted based on the load.
The range of the possible braking pressure applied is specified precisely by the EU (“brake band”). The conventional, rather primitive method currently used in which the braking pressure for empty running is only manually “cut off”, will no longer be permitted in the future.
BPW has therefore filed a patent application for a clever, purely mechanical solution: The brake power of the drawbar trailer can be easily adjusted to the loading condition with a single movement of the hand.
An easily accessible lever controls the power of the brake valve. A scale firmly mounted to the handle indicates the correct locking position for each customer’s individual load condition. The allocation of the scale is calibrated and determined along with the braking calculation by BPW in conjunction with the vehicle manufacturer for each respective vehicle type.
To control the brake force, BPW engineers installed an ALB brake force control, such as is commonly used in spring mounted vehicles. This allows the braking pressure to be controlled manually but precisely across the entire brake band.